1. Field of the Invention
The present invention relates to an obstacle detection apparatus and an obstacle detection program.
2. Background Art
In vehicles, a vehicle-mounted radar is used in a vehicle velocity control system such as an inter-vehicle distance alarm system, a preceding vehicle following system or a collision reducing brake system. As the radar, a millimeter-wave radar is used, for example. Furthermore, the radar is generally mounted in a front portion of a vehicle.
FIG. 5 illustrates an example of a situation where an obstacle 603 is present in front of a host vehicle 601 mounted with a radar 602 in a front portion of a vehicle body. In this example, the front obstacle 603 is another vehicle. Furthermore, in this example, as the radar 602, a radar has horizontal resolution due to a plurality of arrays installed in the horizontal direction; however, it does not have a vertical resolution.
In this case, the radar 602 outputs target data having position information such as a relative longitudinal distance, lateral position and velocity between the host vehicle 601 and the obstacle 603 to a vehicle velocity control system. The vehicle velocity control system performs controls such as a control for maintaining the distance from the obstacle 603, and a control for executing an alarm or velocity reduction in a case where collision with the obstacle 603 is predicted, according to the position information about the input target data.
On the other hand, as shown in FIG. 6, in a case where an obstacle is not present in front of the host vehicle 601, since the target data is not output from the radar 602, the vehicle velocity control system performs a control so that the vehicle regularly runs at a vehicle velocity which is set in advance, and does not execute an alarm.
Here, FIG. 6 illustrates an example of a situation where an obstacle is not present in front of the host vehicle 601 mounted with the radar 602 in the front portion of the vehicle body.
As shown in FIG. 7 and FIG. 8, a case is considered where an obstacle 702 is not present in front of the host vehicle 601, and an elevation-view structure 701 is present.
Here, FIG. 7 illustrates an example of a situation where the obstacle 702 is not present and the elevation-view structure 701 is present in front of the host vehicle 601 mounted with the radar 602 in the front portion of the vehicle body.
FIG. 8 illustrates an example of a scene when viewed from the host vehicle in a case where the obstacle is not present and the elevation-view structure 701 is present in front of the host vehicle mounted with the radar in the front portion of the vehicle body.
The situation, where the elevation-view structure 701 is present and the front obstacle 702 is not present, does not hinder cruising of the host vehicle 601, which is a situation where the vehicle velocity control system is supposed to allow a constant cruising. However, there is a case where the radar 602 outputs target data, as if the front obstacle is present, according to an antenna characteristic and a reflection intensity of the elevation-view structure.
Furthermore, as shown in FIG. 9, when a downward-view structure 711 such as a manhole or a cat's eye is present, or as another example, when a small fallen object such as an empty can is present, cruising of the host vehicle 601 is not hindered in a similar way to the case where the elevation-view structure is present; however, the radar 602 may output target data, as if the front obstacle is present, according to a reflection intensity.
Here, FIG. 9 illustrates an example of a situation where the obstacle is not present and the downward-view structure 711 is present in front of the host vehicle 601 mounted with the radar 602 in the front portion of the vehicle body.
Furthermore, as shown in FIG. 10, in the radar, there is a case where a lateral virtual image is generated according to an antenna characteristic or an angle measurement type.
FIG. 10 illustrates an example of a beam pattern in an azimuth direction (horizontal direction) in a phase detection type radar.
The highest ridge around a position where the AZ (azimuth) angle is 0 degrees is referred to as a main lobe, and different ridges are referred to as a first side lobe, a second side lobe, a third side lobe, and the like as the angle increases. Furthermore, a ridge which occurs at an angle where the phase is reversed by 180 degrees is called a grating lobe.
In the case of the pattern shown in FIG. 10, since a difference in detection level is present between the main lobe, the side lobes and the grating lobes, in the case of an object having a reflection coefficient which is not high, the object is captured by the main lobe; however, it is not detected by the side lobes and the grating lobes.
However, in the case of an object of which the reflection coefficient exceeds the difference in detection level between the main lobe, the side lobes and the grating lobes, such as a large-sized truck 801 in an adjacent lane shown in FIG. 11, the object which is present at angles of the side lobes and the grating lobes is detected in the vicinity of an azimuth angle of 0 degrees. At this time, although the large-sized truck 801 is present in the adjacent lane, the radar may recognize the large-sized truck 801 to be an object in the lane of the host vehicle to output target data. This results in detection of a virtual image.
Here, FIG. 11 illustrates an example of a scene when viewed from the host vehicle in a case where the obstacle is not present and the large-sized truck 801 which results in a virtual image is present in an adjacent lane in front of the host vehicle mounted with the radar in the front portion of the vehicle body. In this example, another vehicle 802 present in front of the host vehicle is not recognized as an obstacle since the distance between it and the host vehicle is large.
Next, an example of a countermeasure against an elevation-view structure or a downward-view structure will be described.
In a general vehicle-mounted radar, an antenna does not have a vertical resolution. Thus, for example, even in the case of an elevation-view structure or a downward-view structure through which a host vehicle can pass, the radar cannot determine the height of the structure, and thus, outputs obstacle data to a control unit.
Thus, as an example, with a configuration in which a plurality of arrays is vertically provided as in the horizontal direction and the angle of incoming waves is calculated by digital beam forming (DBF) or the like, even though the elevation-view structure or the downward-view structure is detected, it is possible to reliably recognize that the structure is not present in front of the obstacle.
However, in such a configuration, problems arise such that the vertical size of the antenna becomes large, a circuit is increased in size as the number of arrays is increased, and the processing load of an arithmetic unit such as a CPU (Central Processing Unit), a DSP (Digital Signal Processor) or an FPGA (Field Programmable Gate Array) is increased as signal processing becomes complicated.
Next, an example of a countermeasure against a lateral virtual image will be described.
As an example, in an array antenna apparatus which includes a transmission array antenna configured of a plurality of antenna elements, a transmission processing unit connected to the transmission array antenna, a reception array antenna configured of a plurality of antenna elements and a reception processing unit connected to the reception array antenna, when any one of the transmission array antenna and the reception array antenna is used as a grating suppressing side and the other one thereof is used as a grating suppressed side, in a state where the angle of a null point on the grating suppressing side and an angle where a grating on the grating suppressed side occurs are set to be equal or close to each other, scanning is performed by a processing unit on the grating suppressing side which performs control so that the grating suppressing side is scanned in synchronization with scanning of the grating suppressed side, while the relationship of the grating on the grating suppressed side and a null point according to the grating is maintained (refer to Japanese Patent No. 4147447).
However, in such a configuration, since a plurality of beam patterns are generated, it is necessary to provide more circuits such as a feeding controller or a timing controller, which incurs costs.
In this regard, although it is considered that the improvement of false detection is possible by a significant change or increase in the size of an antenna, a circuit or the like and by application of a highly complicated process which requires a large load, in a vehicle-mounted radar which for which a small size and low cost are demanded, a countermeasure against the demand is not preferable in many cases.
As a reference, there has been proposed a vehicle detection apparatus including: imaging means for capturing an image in front of a host vehicle, extracting means for extracting a luminance-changed portion of the image as an edge point, vote means for performing a vote in a vote space of a two-dimensional coordinate system based on information regarding of the edge point, detection means for detecting a peak of vote values in the vote space, detection means for detecting coordinates corresponding to the peak as a vehicle, and distance measurement means for measuring the distance and direction to a preceding vehicle, wherein information voted in the vote space is information obtained from horizontal positions of two longitudinal edges located on the image in the horizontal direction, and wherein the peak detection means specifies a range in which the peak of the vote values is detected in the vote space based on the distance and direction data measured by the distance measurement means (refer to Japanese Patent No. 4123138).
In this vehicle detection apparatus, vehicles ranging from a near vehicle to a long vehicle are specified with high accuracy by a monocular camera or a combination of a monocular camera and a radar.
However, in view of the small size and low cost demanded in a vehicle-mounted radar, such a vehicle detection apparatus is not satisfactory.